Search Results

You are looking at 101 - 110 of 3,035 items for :

Clear All

Abstract  

Vinylidene chloride copolymers containing a predominance of vinylidene chloride (85-90%) have long been important barrier polymers widely used in the plastics packaging industry. These materials display excellent barrier to the ingress of oxygen and other small molecules (to prevent food spoilage) and to the loss of food flavor and aroma constituents (to prevent flavor scalping on the supermarket shelf). While these polymers have many outstanding characteristics, which have made them commercial successes, they tend to undergo thermally-induced degradative dehydrohalogenation at process temperatures. The dehydrochlorination occurs at moderate temperatures (120-200C) and is a typical chain process involving initiation, propagation and termination phases. Defect structures, namely internal unsaturation (allylic dichloromethylene groups), serve as initiation sites for the degradation. These may be introduced during polymerization or during subsequent isolation and drying procedures. If uncontrolled, sequential dehydrohalogenation can lead to the formation of conjugated polyene sequences along the polymer mainchain. If sufficiently large, these polyenes absorb in the visible portion of the electromagnetic spectrum, and give rise to discoloration of the polymer. The dehydrochlorination process may be conveniently monitored by thermogravimetric techniques. Both initiation and propagation rate constants may be readily obtained.

Restricted access

thermal decomposition kinetics of magnesite enable us to better understand the decomposition mechanism, control steps, and the various factors on the process of thermal decomposition, thereby allowing us to optimize the thermal decomposition conditions for

Restricted access

protein white to understand its thermal behavior in terms of molecular interaction during its denaturing transition. Therefore, the present study explores the non-isothermal denaturing transition kinetics of the egg protein obtained from the hen's EW using

Restricted access

hydrated form of theophylline-7-acetic acid obtained by recrystallization from water. In particular this study is aimed towards the characterization of the new form as well as providing information on its physical stability and dehydration kinetics

Restricted access

glass transition kinetics of metallic alloys is of great importance to know its thermal stability, and finally to determine the useful range of operating temperatures for a specific technological application before the crystallization takes place [ 4

Restricted access

, and liquefaction processes of biomass as the initial step [ 7 , 8 ]. Hence, knowledge of the characteristics and kinetics of pyrolysis step is vital to predict the behavior of biomass to design and control the necessary conversion units

Restricted access

curing of thermo-setting resins is generally rather complex due to the interaction between chemical kinetics and the simultaneous changes in their physical properties and the development of mechanical properties of the solid material [ 18 ]. The

Restricted access

Abstract  

Cobalt(II), nickel(II), copper(II) and zinc(II) complexes of two new Schiff-bases, citronellal anthranilic acid and citronellal-5-bromoanthranilic acid have been synthesized. On the basis of spectral, magnetic and thermal data, octahedral structure was assigned to all complexes [ML2(H2O)2]. Thermal decomposition of these complexes was studied by TG. Kinetic parameters, viz activation energy, E, pre-exponential factor, A, and order of reaction, n, were calculated from the TG curves using mechanistic and non-mechanistic integral equations.

Restricted access

Abstract  

Although the reaction products are unstable at the reaction temperatures, at a heating rate of 2 deg·min−1 ammonium peroxo vanadate, (NH4)4V2O11, decomposes to (NH4)[VO (O2)2 (NH3)] (above 93°C); this in turn decomposes to (NH4) [VO3 (NH3)] (above 106°C) and then to ammonium metavanadate (above 145°C). On further heating vanadium pentoxide is formed above 320°C. The first decomposition reaction occurs in a single step and the Avrami-Erofeev equation withn=2 fits the decomposition data best. An activation energy of 148.8 kJ·mol−1 and a ln(A) value of 42.2 are calculated for this reaction by the isothermal analysis method. An average value of 144 kJ·mol−1 is calculated for the first decomposition reaction using the dynamic heating data and the transformation-degree dependence of temperature at different heating rates.

Restricted access

degradation kinetics and mechanism of BO6 must be fully understood for successful use in manufacture and elevated temperature applications. Thermogravimetric analysis (TG) has been widely used to determine the kinetic parameters of the degradation

Restricted access